RFC 4880 describes the version 4 signature packet, tag 2, as
- One-octet signature type. - One-octet public-key algorithm. - One-octet hash algorithm. - Two-octet scalar octet count for following hashed subpacket data. Note that this is the length in octets of all of the hashed subpackets; a pointer incremented by this number will skip over the hashed subpackets. - Hashed subpacket data set (zero or more subpackets). - Two-octet scalar octet count for the following unhashed subpacket data. Note that this is the length in octets of all of the unhashed subpackets; a pointer incremented by this number will skip over the unhashed subpackets. - Unhashed subpacket data set (zero or more subpackets). - Two-octet field holding the left 16 bits of the signed hash value. - One or more multiprecision integers comprising the signature.
and i assume that the second to last line means just take the string of the hashed subpacket and hash it with the hash algorithm and take its first 2 bytes. however, no matter what i do, i cannot seem to get it.
I generated this fake key a long time ago
-----BEGIN PGP PUBLIC KEY BLOCK----- Version: BCPG v1.39 mQGiBE5B0h8RBAD533Z5bK1IpBx02QyQL0QoJE4uFRIMGDiwXuwmZzVl+R7Vlurd GRLsCCbE6vOOh7XQVZGzLEBy9WNzZ9m+EbCfSVAYkjS6FhLws6hG6irrnS+b3JBf gFJ8vNGF9Z7bhx+7y7NBk0IMyWkGnUkcnav73t5FQUI2faEBN4c/yAGJZwCgjcB7 3akWk9XVWvTCsiMXxpyvkukEALXsvB6cOoFEtQq9cQHjP63fBlvD94dhhMiM0cH6 hW9JotxdK+cxFGG9ZIWgoN2PWbMJka/H4W5EL6tS+YiNAR7I1Ozkt6X16GjnQUzZ MlSpleK+KiKVN2anRaPEoOIinHrE3ZXd6QlJ/4+OJn4IVWmSEaJpFf4QNgvEu4rh xinyBAD2RNzREOA+wpnFZ4lDt9NZXmXdxQME/l0J9XcvWhpGsxA/MATQKImy7N49 7GT/M38F+TrpBobag1O3buE99fOLyws4Tbc+sZMdHxoiGZDAIRNQS2rv475E6ktj 7vd5CYvOkA6+8sX1+hPcNlkHtHB1OFkJRsYp6k0zkyC9adjBM7QTYWJjIDxtYWtj bUBhYWEuY29tPohGBBMRAgAGBQJOQdIfAAoJEDBSJUXPd92GRSQAoItbtbToOg7a /hcg2sA/aBEQNwuxAKCGR69vmSoCWoBP5waPk0UsjM3BSbjMBE5B0h8QAgCUlP7A lfO4XuKGVCs4NvyBpd0KA0m0wjndOHRNSIz44x24vLfTO0GrueWjPMqRRLHO8zLJ S/BXO/BHo6ypjN87Af0VPV1hcq20MEW2iujh3hBwthNwBWhtKdPXOndJGZaB7lsh LJuWv9z6WyDNXj/SBEiV1gnPm0ELeg8Syhy5pCjMAf9QHehP2eCFqfEwTAnaOlA6 CU+rYHKPZaI9NUwCA7qD2d93/l08/+ZtFvejZW1RWrJ8qfLDRtlPgRzigoF/CXbR iEYEGBECAAYFAk5B0h8ACgkQMFIlRc933YZRrACfUnWTjHHN+QsEEoJrwRvFmvzj bR4An24pTpeeN+I6R59O/sdmYsAhjULX =sStS -----END PGP PUBLIC KEY BLOCK-----
From pgpdump.net, i see that the left 2 bytes of the hash (SHA 1) value is
45 24 for the first signature packet and
51 ac for the second one. i am getting
52 f0 for both. obviously, im not including some information, but what is it? the hashed subpackets are identical, and all of the data before the hashed data are the same as well except they are different types of signature packets (0x13 / 0x18). i have been unable to get either of the correct hash values even when i add/take characters from the data packet. the key im generating is exactly the same as the key shown here except for the hash values.
what is the data that i should be hashing??
the key example up there is made up of
packet 6 + packet 13 + packet 2 + packet 14 + packet 2. i have tried all sorts of combinations of
packet 13, and
packet 2 (from version number to hashed data inclusive), but still cannot find the string that hashes to the correct values
EDIT: From Ilmari Karonen's suggestion that i read section 5.2.4, i still cannot get the answer
i have been using:
a = entire public key packet, header and all b = entire user id packet, header and all c = signature packet '\x04' ... '\x1f' (version ... end of hashed subpacket)
and hashing in all sorts of different ways. Depending on what
hash context and
data (for the user id: is it just the user info, or is it the entire packet? either way i try does not work) mean, the correct method can be anything, which i still cannot find.
how are the hashes of the body and two trailers combined? is that what
hash context defines?